The naturalist David Attenborough once said the creature he finds "most extraordinary" is a nine-month-old human baby. But now he believes the planet can’t sustain many more.
In an interview for BBC Newsnight, the 92-year-old British broadcaster said: “In the long run, population growth has to come to an end. There are some reasons for thinking that will happen almost inevitably.
“But it is very alarming at the rate we’re going, and although people will say, ‘In the long run, we are going to stabilize’, they’re going to stabilize - as far as I can see - at a rather higher level than the Earth can really accommodate.”
Roughly 83 million people are added to the world's population each year, according to the UN, with modern advances in medicine and nutrition to thank for their survival into adulthood and old age.
But while fertility levels (and birth rates) are dropping globally, the overall trend is continued population growth, with increasing pressure on the planet’s limited resources - and impact on the environment.
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Why should we take note?
Attenborough, whose 2015 interview by Barack Obama about climate change was screened in more than 50 countries, has contributed a huge amount to shaping our views on environmental issues. As UN Head of Environment Erik Solheim says, “few people have inspired action for the planet” like him.
When Blue Planet II aired in November 2017, featuring an episode on the ocean’s plastic problem, some 80 million people in China alone tuned in.
Now, it seems Sir David is turning his attention to the issue of overpopulation and the world should take note.
Spend just a minute watching the world population counter tick up on Worldometers and you’ll see just how quickly we’re swelling in numbers. The current figure stands at around 7.7 billion, and this is projected to become 9.8 billion by 2050, according to the UN.
China and India are the most populous nations on the planet, with 1.4 billion and 1.3 billion people respectively, according to the UN’s World Population Prospects.
By around 2024 though, India will have overtaken China, while Nigeria, currently the world’s seventh largest country, is growing the fastest - and is predicted to overtake the United States to become the third largest country before 2050. Japan, by contrast, is seeing its population decline, which is impacting on its economy.
While it’s true that global fertility levels are in decline, leading to a slowing in overall population growth, fertility in the world’s 47 least developed countries is still relatively high - at 4.3 births per woman between 2010 and 2015 - meaning rapid growth of these countries at 2.4% per year.
According to the UN, the populations of 26 African countries are due to at least double in size between 2017 and 2050. As the review notes, such growth represents a “considerable challenge” to governments trying to implement the UN’s Sustainable Development Goals, including ending poverty and hunger.
While the birth rate is still growing in some areas, life expectancy is also a major factor when it comes to population growth.
Attenborough notes: “One of the reasons population has increased as fast as it has, is that people like me are living longer than we did, so there are more and more people just because the expectancy of life has increased.”
The number of people aged 60 and over is predicted to double between 2017 and 2050 - from 962 million to 2.1 billion globally.
Earth’s carrying capacity
More people means more carbon footprints - more cars, waste and emissions, more houses and infrastructure to be constructed using the world’s limited resources, more mouths to be fed using more water and energy in food production. So, how many people is too many?
Scientists are still undecided on the Earth’s "carrying capacity" - the maximum number of people it can support indefinitely - with estimates ranging widely between 500 million and more than one trillion.
Part of the reason is that our consumption of resources varies massively across the globe.
“An average middle-class American consumes 3.3 times the subsistence level of food and almost 250 times the subsistence level of clean water,” according to Professors Stephen Dovers and Colin Butler in their paper, Population and Environment: A Global Challenge.
“So if everyone on Earth lived like a middle-class American, then the planet might have a carrying capacity of around 2 billion. However, if people only consumed what they actually needed, then the Earth could potentially support a much higher figure.”
As developing countries catch up with the rest of the world, you might think their carbon footprint grows at the same rate, but, according to research, between 1980 and 2005, many of the nations with the fastest population growth rates had the slowest increases in carbon emissions.
Earth Overshoot Day
Ecological overshoot is a key concept in footprint science and happens when we turn resources into waste faster than the planet can resupply them. For example, we’re burning through fossil fuels that took millions of years to form at rates far greater than Earth can replace them.
Since 2006, the think tank Global Footprint Network has marked Earth Overshoot Day - the day when humanity has used up nature’s resource budget for the year. In 2018, it was held on August 1, the earliest date it has been since the world went into overshoot in the 1970s - meaning we’re using up 1.7 Earths every year.
“Our current economies are running a Ponzi scheme with our planet,” Mathis Wackernagel, CEO and co-founder of Global Footprint Network, said.
“We are borrowing the Earth’s future resources to operate our economies in the present. Like any Ponzi scheme, this works for some time. But as nations, companies, or households dig themselves deeper and deeper into debt, they eventually fall apart.”
What can be done?
Governments recognise the severity of the situation and have mostly come together over global policies like the UN’s Paris Agreement, to limit carbon emissions and their impact on climate change. In addition, new technologies are being developed to make our use of resources more efficient.
As for controlling population growth, the education of women is one key factor. Research shows the higher level to which a woman is educated, the fewer children she is likely to have. In Ghana, for example, women who have been to high school, have a fertility rate of between two and three children, compared with six for those who have no education.
This could be for several reasons including learning about desired family size and understanding child health better. This means that the mother is more confident her children will survive. She is also likely to hold more sway within the family, arguing for fewer children if that is what she wants.
There is also plenty that individuals can do to reduce their personal footprint.
The Global Footprint Network calculates that moving Earth Overshoot day back by five days every year would mean that, by 2050, we’d be using the resources of less than one planet. Just eating 50% less meat and replacing it with vegetarian alternatives could save the planet five days.
As David Attenborough says, if we want to save Earth, we can no longer afford to keep eating meat: “We are omnivores, so biologically, if you could have a biological morality, you can say, yes we evolved to eat pretty well everything.
“But now we’ve got to a stage in our own social evolution in which that is no longer practical.”
Sir David says he himself now eats less meat and is bolstered by the knowledge that it’s helping the planet.
Population growth and the depletion of Earth’s resources is a truly global problem. But it’s also something where small individual actions will together help to ensure a better future for the planet.